The control of the α-Al2O3 polymorph in industrial scale was achieved in the beginning of the 1990's with commercial products based on U.S. Pat. No. 5,137,774. Later modifications of this patent have been used to deposit α-Al2O3 with preferred textures. In U.S. Pat. No. 5,654,035 an alumina layer with the (10 12) texture and in U.S. Pat. No. 5,980,988 an alumina layer with the (11 20) texture are disclosed. In U.S. Pat. No. 5,863,640 the (10 12), (10 14) and (11 20) textures are disclosed. U.S. Pat. No. 6,333,103 describes a modified method to control the nucleation and growth of α-Al2O3 on the (10 1(10)) plane. U.S. Pat. No. 6,869,668 describes a method to obtain a strong (10 10) texture in α-Al2O3 using a texture modifying agent (ZrCl4). The prior-art processes discussed above use all deposition temperatures of about 1000° C. U.S. Pat. No. 7,094,447 describes a technique to achieve a pronounced (10 12) texture. Enhanced deposition techniques to produce pronounced (10 14) and (11 26) textures are disclosed in US2006/0199026 and US 2006/0141271, respectively. However, the (0006) diffraction peak, which is an indication of the (0001) texture, has not been observed earlier. In US 2007/104945 a (0001) textured alumina layer is disclosed. The (10 12), (10 14) and (0001) textured alumina layers are compared and the (0001) texture is found superior to the other textures.
Methods to produce a tough binder phase enriched surface zone in the upper part of cemented carbide cutting tool inserts prior to coating are commonly referred to as gradient sintering. There are two types of processes used to produce the binder phase enriched surface zone:    (i) By dissolution of cubic carbide phase near the surface (N-gradient), e.g., U.S. Pat. Nos. 4,277,283, 4,610,931, 4,830,930 and 5,106,674.    (ii) By controlled cooling or decarburisation (C-gradient), e.g., U.S. Pat. No. 5,106,674 and U.S. Pat. No. 4,830,930
New laws/regulations will increase the cost of the use of cooling lubricants in metals machining. This promotes dry machining. In turn, this will increase the demand for more temperature-resistant coated cemented carbides and generally forces the metal cutting industry to consider new alternative methods. The following are the most important trends in the market place:                Higher cutting speeds, for increased productivity.        Dry machining and/or Minimal Quantity of Lubrication (MQL), for reduced costs and environmental aspects.        Difficult-to-machine materials, i.e., high strength materials, for lighter components and constructions.        
All these trends put more demands on wear resistance, together with deformation resistance and toughness. Due to its high chemical stability and favourable thermal properties Al2O3 is the ideal coating material for high-speed metal cutting. Due to the trends in the market place discussed above the need for enhanced wear resistance together with enhanced toughness is highlighted.
The present invention is directed to these and other important needs, including providing an improved alumina coated cemented carbide tool with improved on wear resistance, together with deformation resistance and toughness.